Spectroscopic and Computational Assessment of Silicon’s Electrophilicity in Phosphinosilylium Cations

An experimental method of determining
the electrophilicity of silicon
in phosphinosilylium cations is reported and compared to Djukic’s
DFT method of computing relative intrinsic silylicity, Π. We
also establish linear correlations between silicon electrophilicity
and 29Si NMR chemical shifts, DFT-computed silylicities,
and the Tolman electronic parameter of the phosphine. These correlations
were not universal, as deviations were observed for the most sterically
hindered phosphines. Intermolecular silylium transfer experiments
between phosphinosilyliums and added phosphines provided a thermodynamic
assessment of the electrophilic character at silicon. This confirmed
that relative intrinsic silylicity (Π) and 29Si NMR
chemical shifts are useful parameters for semiquantitatively determining
the electrophilicity of the silyl group in a Lewis pair.